1. Field of the Invention
The present invention relates to a stereoscopic image display method and a stereoscopic image display apparatus using the method and, more particularly, to a stereoscopic image display apparatus capable of causing an observer to see a stereoscopic image within a wide observation region without using any special glasses.
2. Related Background Art
Conventionally, as a stereoscopic image display apparatus not using any glasses, a lenticular lens type apparatus and a parallax barrier type apparatus are proposed.
In these two types of apparatuses, a lenticular lens or a parallax barrier is arranged on the surface of a liquid crystal display. For this reason, the image quality degrades due to surface reflection from the lens surface, or the black matrix of the liquid crystal display generates a Moire, resulting in an eyesore.
In addition, in these types, a stripe image must be combined by alternately arranging stripe pixels of two parallax images, and the combined image must be displayed. For this reason, the resolution of the stereoscopic image display apparatus is decreased to at least 1/2 that of the image display means.
A stereoscopic image display apparatus solving these problems is disclosed in Japanese Laid-Open Patent Application Nos. 5-107663 and 7-234459.
FIGS. 22A to 22C are views showing the basic arrangement of the stereoscopic image display apparatus disclosed in Japanese Laid-Open Patent Application No. 5-107663. This apparatus comprises an optical directivity changing apparatus 101 having a matrix type surface illuminant 102 and a lenticular sheet 103, and a transmission type display apparatus 104. While a stripe light source (102R in FIG. 22B) for the right eye is turned on, an image (104R in FIG. 22C) for the right eye is displayed in an odd number frame. While a stripe light source (102L in FIG. 22B) for the left eye is turned on, an image (104L in FIG. 22C) for the left eye is displayed in an even number frame.
Since all pixels are used in the even and odd number frames, an apparatus which does not require division of the pixels and prevents a decrease in resolution can be realized.
However, in the apparatuses of these types, the observer can see the stereoscopic image only within a range corresponding to a binocular center distance of about 65 mm. For this reason, the observer must fix the head position during observation, resulting in difficulty in observation.
In a scheme proposed in Japanese Laid-Open Patent Application No. 2-44995, a lenticular lens is supported to be movable in the horizontal direction, and the positions of both eyes of the observer are detected. The lenticular lens is moved in the left-and-right direction relative to the display element in accordance with the detection result, thereby widening the stereoscopic image region. Japanese Laid-Open Patent Application No. 2-50145 proposes a scheme in which the positions of the eyes of the observer are detected, and the left and right positions of the display pixel portions of an image are replaced, thereby widening the stereoscopic image region.
Of these conventional arts, in the method of time-divisionally displaying the right-eye parallax image and the left-eye parallax image to obtain a stereoscopic image, images must be changed over at a high speed to prevent flicker.
Isono et al. have reported "Conditions for forming a time-division stereoscopic vision" (Journal of the Society for Television, Vol. 41, No. 6 (1987), pp. 549-555). According to this, no stereoscopic image can be formed by time division using a field frequency of 30 Hz.
The critical frequency (critical fusion frequency CFF) at which no flicker is perceived when the left and right eyes are alternately closed is about 55 Hz. From the viewpoint of flicker, the field frequency must be at least 110 Hz.
Therefore, in these conventional arts, a display device capable of displaying an image at a high speed must be used as the transmission type display apparatus 104.
Of these conventional arts, the scheme of measuring the observer position to follow the movement of the observer can cope with only horizontal changes in observer position. When the distance between the observer and the stereoscopic image display apparatus changes, crosstalk is generated to degrade the stereoscopic effect.
When a member such as a lenticular lens is to be actually moved to follow the movement of the observer, such a relatively large member must be precisely moved by a small amount like the pixel pitch or lenticular pitch. This requires a complex and precise driving system, resulting in an expensive apparatus.
When the left and right display pixel portions are replaced to cause the stereoscopic image observation region to follow the movement of the observer, as in Japanese Laid-Open Patent Application No. 2-50145, the unit of follow-up movement almost equals the distance between the eyes of the observer, so that this method cannot cope with fine movement of the observer.